Design of Nanocomposite Low‐Friction Coatings

Abstract

Friction and wear between moving surfaces is unavoidable and is an important reason for failure of mechanical components. A wear‐resistant and low‐friction coating can prolong the lifetime of an engineered component. Here we demonstrate a new concept for the design of low‐friction nanocomposite carbide coatings with an intrinsic driving force to form amorphous carbon (C–C bonds). Ti–Al–C has been chosen as a model system, but the idea is general and should be applicable to a wide class of materials. The ability to intrinsically form amorphous carbon is achieved by a substitutional solid solution of the weak‐carbide‐forming metal (Al) into the thermodynamically stable monocarbide (TiC). This creates, in a controllable manner, a driving force for phase separation of carbide particles embedded in a matrix of amorphous carbon. In a tribological contact the amorphous carbon can be further graphitized and thereby lower the friction coefficient. Consequently, the model system has a self‐lubricating mechanism but at the same time a tunable share of the two phases, which gives excellent possibilities to design wear resistance and toughness. In this paper we show that the friction coefficient can be lowered by more than 50 % for Al‐containing TiC coatings without severe loss in mechanical characteristics.

Carbide and nanocomposite thin films in the Ti–Pt–C system

“…The relative amount of a-C phase increases with Pt-content. This observation is consistent with observations from the Ti-Al-C, Ti-Fe-C, and Ti-Ni-C systems, where the solid solution of a weak carbide former in TiC x was found to promote the formation of a-C phase during deposition [15][16][17]27]. The formed (Ti 1-x Pt x )C y is not a thermodynamically stable compound and is likely to decompose upon annealing considering the position of Pt in the periodic table and the lack of PtC x at normal conditions.…”

Control of crystallinity in sputtered Cr–Ti–C films

“…Typically, the group IV metals Ti, Zr, and Hf form crystalline films although the carbide often is present as nano-sized crystallites in an amorphous carbon (a-C) matrix, depending of the C content. The properties of these nanocomposites are typically affected by the relative amount of a hard carbide phase in a softer a-C matrix [4][5][6][7]. For the 3d transition metals, the tendency to form amorphous films increases with increasing number of d-electrons in the metal and sputtered Cr-C and Fe-C films are therefore often amorphous [8][9][10][11].…”

Tailoring microstructure and phase segregation for low friction carbon-based nanocomposite coatings

“…However, it would inevitably cost some hardness of the coatings due to its softness. [27][28][29][30][31] Besides, Wilhelmsson et al 32 reported that the soft metal Al, which formed a substitutional solid solution at the Ti sites in cubic TiC coating, created a situation of a driving force for carbon phase separation from the carbide particles. Unfortunately, they didn't consider a study on the placing of a solid solution of this WCF Al into the DLC matrix.…”